The proposed studies will continue our work in modeling the branched chain amino acid leucine and its Alpha ketoacid, Alpha ketoisocaproate (KIC), in vivo. Using the immature pig as a model, we intend to fully define the isotopic-nutritional model necessary to evaluate hormonal effects on proteolysis during absorption of a meal. Using [1-18OH] leucine, of which only half is incorporated into proteins, and dipeptide tracers, which are hydrolyzed intracellularly, it will be possible to more closely approximate intracellular specific radioactivity and minimize recycling of tracers through protein. This optimized model will then be validated by attempting to measure the absorption of diet infused into the small intestine. Once the appropriate isotopic model has been validated it will then be used to define the optimal dietary treatments necessary to maximize the effects of increasing and decreasing proteolysis on meal amino acid use. An amino acid deficient diet, a diet adequate in all amino acids, and an amino acid excessive diet will be evaluated. Results from these studies will define a sensitive model which can accurately measure leucine entry into protein, oxidation, proteolysis, and absorption. Finally, this optimized model will be used to examine the effects of growth hormone, insulin, glucagon, T3, cortisol, epinephrine, and prostaglandin E2 on meal-related protein deposition. This isotope method will be compared to direct measurements of whole body leucine balance and nitrogen balance. Together these studies will develop and validate an optimum model for examining proteolysis and protein synthesis during meal absorption. This model will then be used to examine the impact of changes in hormone status on protein synthesis and proteolysis during meals.